1. Field of the Invention
The present invention relates to a paper-releasing guide-claw for a copying machine and a method for producing the same. More specifically, the invention relates to a method for producing a paper-releasing guide-claw for a copying machine having excellent dimensional stability and heat distortion resistance at high temperatures.
2. Description of the Prior Art
Dry process copying machines usually form electrostatic latent images corresponding to characters and graphics on a surface of a photosensitive drum. The latent images are converted to toner images and transferred onto a surface of paper supplied from a paper feeding cassette. Thereafter the transferred toner images are fixed on the surface of paper. A mechanism is integrated into the copying machines so that the paper surface is hot pressed with a heated fixing roller whereby the molten toner images are adhered to the fiber of the paper. Such heat fixing prevents removal of the toner from the surface of the paper. After passing through the fixing roller, the copying paper must be ejected without being wound around the roller. A guide-claw is employed to scoop up the edge of the copying paper. The head of the guide-claw contacts the peripheral surface of the fixing roller.
It is necessary that a paper-releasing guide-claw have the following properties:
(a) low frictional resistance to the peripheral surface of the roller to insure that the roller surface is not damaged;
(b) good mechanical strength and high temperature stiffness;
(c) the toner must not adhere to the guide-claw.
Recently developed copying machines are capable of producing copies at a higher speed than prior art machines. The heating temperature of the fixing roller is often set at higher levels for faster copying machines. Thus the paper-releasing guide-claw must have a heat resistance of at least 250.degree. C., in some cases at least 300.degree. C.
Various methods have been proposed to date for improving non-tackiness of the paper-releasing guide-claw toward printing toners. It has been proposed to add improvers such as a fluoro resin to materials from which paper-releasing guide-claws are made or to form a film from a fluoro resin or low molecular weight polymer of a specific fluoro resin, to the surface of the guide-claw.
Japanese Patent Publication No. 23554/1986 discloses a method for preparing a paper-releasing guide-claw of a copying machine. The method comprises molding a polyamide-imide into a prescribed shape, subjecting the molded paper-releasing guide-claw to heat treatment, followed by coating the surface of the molded product with a fluorine containing resin, and then baking the coated product. It is reported in the above publication that the paper-releasing guide-claw thus obtained has improved heat resistance over conventional paper-releasing guide-claws and can resist temperatures above 200.degree. C.
Japanese Patent Laid-Open No. 60737/1988 discloses a method for preparing a paper-releasing guide-claw which comprises molding a polyamide-imide resin into a prescribed shape, coating the surface of the molded product with a fluorine containing resin, and then heat treating the coated resin. This method decreases the number of steps of the method described in Japanese Patent Publication No. 23554/1986 and provides a paper-releasing guide-claw resistant to temperatures up to 250.degree. C.
The above two methods employ polyamide-imide. Polyamide-imide contains polyamic acid linkages prior to molding and thus has residual thermoplasticity. Imidization by dehydration and heat curing are carried out which enhance heat resistance.
However, improvement of heat distortion resistance essentially depends upon the type of heat resistant resin used a the material for the paper-releasing guide-claw. Representative exemplary materials used for producing the guide-claw include polyamide-imide, polyphenylene sulfide, polyether ether ketone, polyether ketone, polyether sulfone, polyetherimide, polysulfone and aromatic polyester.
Amorphous resins such as polyether sulfone, polyetherimide and polysulfone have glass transition temperatures lower than 250.degree. C. Softening of resins commences at such glass transition temperatures and thus the heat resistance of these resins is low.
On the other hand, polyphenylene sulfide, polyether ether ketone and polyether ketone are crystalline resins. The heat resistance of these resins can be improved to some extent by compounding high-temperature resistant fibers such as glass fibers and carbon fibers into these resins or by adding inorganic powdery fillers such as mica and talc to these resins. However, when heated above 300.degree. C. by the fixing roller, the head of the paper-releasing guide-claw contacting the roller is gradually deformed which causes a problem of severe reduction in the releasing function. Japanese Patent Publication Nos. 23554/1986 and Laid-Open No. 60737/1988 disclose that polyamideimide has a heat resistance of about 250.degree. C. when used as a paper-releasing guide-claw, however, the head of the guide-claw gradually deforms at a temperature of about 300.degree. C. and lowers its releasing function.
Polyimide resins are noteworthy only with respect to their heat resistance. Many polyimide resins that exhibit excellent properties have been developed to date. These resins, however, are generally brittle, insufficient in high temperature impact strength, and hard to mold because they are insoluble in solvents and have high softening temperatures. For example, polyimide resins consisting of a primary chain of the formula (I): ##STR2## (Trademark; KAPTON and VESPEL, Products of E. I. Du Pont de Nemours & Co.) have no distinct glass transition temperature and are excellent in high-temperature resistance. When such resins are used for molding materials, the hot molding process is difficult and thus is unsuitable for use in practical applications.